std ::对std :: string和自定义类无法复制到std :: map :: insert（std :: make_pair（string，class））

Question

This error:

error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const std::string' (or there is no acceptable conversion)  c:\program files (x86)\microsoft visual studio 10.0\vc\include\utility  216

occurs on this function's only line:

void Animation::AddAnimation(std::string name, AnimationFrameSet& animation) {
    _animations.insert(std::make_pair(name, animation));
}

_animations is a std::map<std::string, AnimationFrameSet>

AnimationFrameSet declares an operator=(...) and a copy constructor, but weirdly enough, the compiler says it fails on the attempted copying of const std::string ...even though the string isn't even being passed in as a const .

I can't for the life of me figure out (or even remember! :P) why this is/should throwing/throw an error.

Thanks.

EDIT

The reason I'm a little confused why this is not working is that a different class uses a very similar implementation and it does not throw an error:

BITMAP* BitmapCache::GetBitmap(std::string filename) {
    //Return NULL if a bad filename was passed.
    if(filename.empty()) return NULL;
    if(exists(filename.c_str()) == false) return NULL;

    //Reduce incorrect results by forcing slash equality.
    filename = fix_filename_slashes(&filename[0]);

    //Clean the cache if it's dirty.
    CleanCache();

    //Search for requested BITMAP.
    MapStrBmpIter _iter = _cache.find(filename);

    //If found, return it.
    if(_iter != _cache.end()) return _iter->second;

    //Otherwise, create it, store it, then return it.
    BITMAP* result = load_bmp(filename.c_str(), NULL);
    if(result == NULL) return NULL;
    /*Similar insert line, a non-const std::string that was passed in is passed to a std::make_pair(...) function*/
    _cache.insert(std::make_pair(filename, result));
    return result;
}

typedefs:

typedef std::map<std::string, BITMAP*> MapStrBmp;
typedef MapStrBmp::iterator MapStrBmpIter;

Answer 1

Since _animations is a std::map , try using another method of inserting, such as:

_animations[name] = animation;

But the more important thing to check would be if the AnimationFrameSet class does have a valid copy constructor and assignment operator. If it doesn't you may want to use a smart pointer class such as:

typedef std::shared_ptr<AnimationFrameSet> AnimationFrameSetPtr;

Then the map would be:

std::map<std::string, AnimationFrameSetPtr>

Answer 2

The reason why this is failing is because the std::map container you are using expects a const value as key value.

Check the documentation of std::map here .

Example:

class TestClass
{
};

std::map< const std::string, TestClass > myMap;
std::pair< const std::string, TestClass > firstElement = std::make_pair("test", TestClass() );
myMap.insert( firstElement );